Flexible pipes of the present type are well known in the art in particular for offshore transportation of fluids. Such pipes usually comprise an inner liner, also often called an inner sealing sheath or an inner sheath, which forms a barrier against the outflow of the fluid which is conveyed through the pipe, and one or more armoring layers e.g. of metal, such as steel on the outer side of the inner liner (outer armoring layer(s)). The flexible pipe usually comprises an outer sheath provided with the object of forming a barrier against the ingress of fluids from the pipe surroundings to the armor layers.
Typical unbonded flexible pipes are e.g. disclosed in WO0161232A1, U.S. Pat. Nos. 6,123,114 and 6,085,799.
In order to have sufficient strength, in particular to prevent the collapse of the inner sealing sheath, the flexible pipe may for certain applications comprise an armor layer located inside the space defined by the inner sealing sheath. Such inner armoring layer or layers are normally referred to as a carcass.
In this text the term “unbonded” means that at least two of the layers including the armoring layers and polymer layers are not bonded to each other. In practice the known unbonded, flexible pipe normally comprises at least two armoring layers located outside the inner sealing sheath, which armoring layers are not bonded to each other neither directly nor indirectly via other layers along the pipe. The pipe layers can therefore move with respect to each other, and thereby the pipe becomes bendable and sufficiently flexible to roll up for transportation and to withstand the high mechanical forces it may be subjected to in use.
The above-mentioned type of unbonded, flexible pipes is used for dynamic as well as for static offshore applications for the transport of fluids and gases, in particular crude oil and gasses.
Transportation of crude oil and gas products often results in difficulties due to the lack of control of the temperature. If the temperature is too high, the polymer materials of the flexible pipe may degrade, and if the temperature is too low, a number of undesired effects have been observed including                undesired increase in viscosity, which reduces the flow rate in the pipe;        precipitation of dissolved paraffin and/or flocculation of asphaltenes which then increases the viscosity of the product, and        once deposited can reduce the effective inside diameter of the pipe; and        obstruction of the pipe due to sudden, compact, and massive formation of gas hydrates which precipitate at high pressure and low temperature.        
It is well known to seek to avoid some of the undesired effects by using flexible pipes with thermal insulations thereby reducing heat loss of fluids flowing in the bore of the pipes e.g. as described in U.S. Pat. No. 6,530,137, US20090101225 and EP0400689
U.S. Pat. No. 6,530,137 describes a heat-insulated flexible pipe comprising at least one layer of rigid and extruded insulating material on the outside of said pipe. The layer comprises means for restoring the flexibility of the insulated pipe in the form of at least one circumferential slot.
US20090101225 describes a flexible pipe body and a method of providing a flexible pipe is disclosed. The flexible pipe body includes a fluid retaining layer, at least one tensile armor layer, at least one extruded thermal insulation layer over an outermost one of the at least one tensile armor layers and an outer shield layer over the insulation layer.
EP 0400689B1 describes a thermally insulating structure around a central or tube core. It comprises, around the said internal or tube core, a plurality of annular partitions, distributed along the length of the core and integral with this, a thermally insulating material filling the annular chambers in between the front faces of the successive partitions and the outer covering of the inner core, and a continuous, extruded, outer sheath.
The object of the invention is to provide an insulated, unbonded, flexible pipe which is simple to prepare, can be prepared in a cost-effective manner and has an effective insulation which simultaneously does not result in an unacceptable reduction of the flexibility of the pipe.